Method of resisting corrosion in metal reinforcing elements contained in concrete and related compounds and structures

ABSTRACT

A method of resisting corrosion of metal elements in concrete is provided. It includes introducing into concrete containing metal elements, at least one combination compound capable of sequestering chloride ions having the formula 3Me(II)O.(R, R′) 2 O 3 .Me(II)(anion) 2 .nH 2 O, where R and R′ are different and are independently selected from the group consisting of Al, Fe and Cr; anion is selected from the group consisting of NO 2 , NO 3  and OH, n is 0 to 24, and Me(II) is a cation and is selected from the group consisting of Ca, Ba, Sr, Mn, Zn and combinations thereof. In one embodiment of the invention, concrete structures may be rehabilitated by providing an overlay containing the combination compound, with the overlay being provided in situ or as a preformed member and with possible use of a slurry in combination with an overlay segment.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. Ser. No.10/047,226, filed on Jan. 14, 2002, which is a continuation-in-part ofU.S. Ser. No. 10/044,660, filed Jan. 9, 2002, which is acontinuation-in-part of U.S. Ser. No. 10/010,581, filed Nov. 13, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to a method of introducing intofresh concrete, as herein defined, compounds capable of sequesteringchloride ions to establish resistance to corrosion of metal reinforcingelements contained within or contacting the concrete and provide acorrosion resistant oxide layer on the metal reinforcing elements, aswell as related compositions and structures. The invention is alsodirected toward corrosion protection of concrete articles wherein theconcrete has already set and hardened.

BACKGROUND INFORMATION

[0003] The advantageous use of metal reinforcing members, such as steelreinforcing members, in concrete for structural uses has been known formany years. Concrete is known to provide desired compressive strength,but tends to lack tensile strength. The reinforcing bars co-act with theconcrete to provide enhanced tensile strength for the combination ofmaterials. It has also been known to employ corrugated metal deck incombination with concrete to create a composite with similar benefits.Numerous other metal members have been embedded in concrete or providedin contact therewith to achieve enhanced benefits in the structuralenvironment as a result of such materials. Among these additionalmaterials are grids, beams, bolts, hold-downs and wire mesh.

[0004] One problem with such construction has arisen as a result ofexposure of concrete to salts, such as calcium chloride and sodiumchloride, on external structural members to resist the undesiredaccumulation of snow and ice on bridges and other concrete paved areassuch as roadways, parking lots, sidewalks and the like. While thesechloride salts do provide benefits in terms of de-icing of concretesurfaces, they frequently result in the chloride solutions migratinginto the concrete decks and adjacent vertical concrete surfaces, such aswalls and columns, also subjecting these to chloride intrusion. Also,saline seawater may migrate into the pores of concrete exposed toseawater as in sea walls, With respect to bridge decks, in particular,an enhanced problem results from air movement under the deck creating anenvironment wherein the salts are aspirated into the concrete and saltladen solutions flow into the pores.

[0005] Regardless of the manner in which chloride enters such concrete,the chloride, upon reaching the steel reinforcing members, tends toaccelerate corrosion of the same because the oxidation of the metalmetallic iron to Fe²⁺ is catalyzed by the chloride. Also, oxides andhydroxides of Fe²⁺ frequently form and occupy porosity in the vicinityof the interface of the steel and concrete. In addition, oxides andhydroxides of Fe³⁺ may also be produced. As these iron oxides andhydroxides are of greater volume than the iron metal from which theywere produced, they tend to cause internal stresses which may becomehigh enough to crack the concrete, and also degrade the desired bondbetween the metal reinforcing elements and the concrete.

[0006] U.S. Pat. No. 5,049,412 discloses a method of re-alkalizingconcrete in which carbonation has occurred. An outer layer of theconcrete structure containing reinforcement which layer through exposureto air has been carbonated has an adjacent layer that remains relativelyless carbonated. The patent discloses applying to the outer surface awater type adherent coating followed by introducing between the outeradjacent layers, water from a source external to the concrete structureand maintaining the concrete structure in this condition for a period oftime sufficient to effect diffusion of the alkaline materials from therelatively less carbonated adjacent layer into the relatively carbonatedouter layer.

[0007] U.S. Pat. No. 5,198,082 discloses a process for rehabilitation ofinternally reinforced concrete, which includes temporary application ofan adhered coating of an electrode material to surface areas of theconcrete. Distributed electrodes such as a wire grid is embedded in thecoating. A voltage is applied to the reinforcement and distributed tothe electrode to cause migration of chloride ions from the chloride intothe electrolytic coding. Among the shortcomings of this approach is theneed to provide, at the local source, a source of electrical power. Thiselectrical equipment might have to be maintained at the site forextended periods of time. This further complicates matters byestablishing a risk of injury to children and others that might find theequipment at an attractive nuisance, as well as the risk of theft andvandalism. Also, such chloride extraction processes may alter theconcrete microstructure by making it more porous and permeable, thereby,facilitating enhanced re-entry of chloride when de-icing salts are againapplied to the exterior.

[0008] It has been known to employ nitrites, such as calcium nitrite, inresisting corrosion of steel parts in concrete. It is believed that thenitrites oxidize the Fe²⁺ to Fe³⁺ which, in turn, precipitates as Fe₂O₃.The Fe₂O₃ thus formed tends to act as a barrier to further contactbetween the chloride and the steel. See, generally, U.S. Pat. Nos.4,092,109 and 4,285,733. Neither calcium nitrate nor Fe₂O₃, however,function to sequester chloride. The latter provides merely a barrier.

[0009] There remains, therefore, a very real and substantial need for amethod and related composition and structure which will resist undesiredcorrosion of metal structural elements contained within, or in contactwith, concrete structural members.

SUMMARY OF THE INVENTION

[0010] The present invention has met the above-described need.

[0011] The method, in one embodiment, includes resisting corrosion inconcrete containing metal reinforcing elements composed of steel,copper, galvanized steel, tin plated steel or other structurallysuitable metals by introducing into fresh concrete containing metalreinforcing elements at least one compound capable of sequesteringchloride ions in a low solubility compound.

[0012] In connection with steel reinforcing elements, a low solubilitycompound within which the chloride ions are sequestered preferably alsois created in a reaction that releases nitrite, which serves to oxidizeFe²⁺ to thereby provide a corrosion-resisting oxide layer on the steelreinforcing elements. This, therefore, in connection with steel achievestwo levels of corrosion resistance, one of which is the actual capturingor sequestering of the potentially damaging chloride ions, and thesecond of which provides a protective layer on the metal reinforcingelements.

[0013] Among the preferred compounds for use in the method of thepresent invention are one or more compounds selected from the groupconsisting of (1) 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O; (2)3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O; (3) 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O; and (4)3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O, wherein n=0 to 24 and preferably 10 to 18,depending upon the relative humidity to which a compound isequilibrated. If desired, lower values of “n” may be obtained by dryingat low relative humidity as by evacuation or by heating, for example.

[0014] A further compound employed in another embodiment of theinvention is, 3Me(II)O.R₂O₃.Me(II)(anion)₂.nH₂O wherein Me(II) is one ormore divalent cations, such as Ca, for example, R₂ is Al₂, Fe₂ or Cr₂anion is NO₂, NO₃, CO₃, BO₄ or OH and n is 0 to 24, and preferably 10 to18. For some formulations, the anion may be divalent. In this case theformula would be Me(II)O.R₂O₃.Me(II)(anion).nH₂O wherein n is 0 to 24and preferably 10 to 18.

[0015] The invention also contemplates a concrete structure which hashydrated fresh concrete and a plurality of metal structural elements incontact with the hydrated fresh concrete with a compound whichsequesters chloride ions dispersed within the concrete.

[0016] The invention in another embodiment contemplates rehabilitationof existing concrete structures by providing a chloride sequesteringcompound in a member adjacent to the concrete structure and having acomposition such that migration of chlorine ions away from metalstructural elements in the concrete structure and into the adjacentoverlay may be effected. In addition, if desired, release of nitrite tomigrate into the concrete structure and afford corrosion protection toembedded steel.

[0017] In one version, the overlay, which may be formed in situ or as apreformed panel, contains the chloride-sequestering compound. Inanother, a slurry may be applied to the concrete structure with orwithout an overlay secured thereover.

[0018] The invention also contemplates in situ formations of the desiredcompounds which are suitable for chloride ion sequestration and nitriterelease in order to establish an oxide protective layer over the metalelements.

[0019] The compound may be formed by adding certain materials to freshconcrete with a reaction product of cement hydration yielding a furthercomponent or separately adding the component. The in situ concept mayalso be employed in remediation of existing concrete structures.

[0020] Alternate sources of aluminum for use in creating the compoundmay be provided.

[0021] In another approach, sources of calcium and aluminum may beprovided separately or as an admixture introducing the desired compound.

[0022] It is an object of the present invention to provide a method andrelated compounds and structures for inhibiting corrosion of metalelements positioned within or in contact with concrete in a structuralenvironment.

[0023] It is a further object of the present invention to provide such asystem wherein undesired chloride ions will, as a result of a reaction,be sequestered, thereby reducing their ability to corrode the metalelements.

[0024] It is yet another object of the invention to, through a reactioneffecting such sequestration of ions, to provide free nitrites whichwill oxidize the Fe²⁺ ions produced during the corrosion process to Fe³⁺ions which, in turn, precipitate as Fe₂O₃ which coats the metal elementand, thereby, resists corrosion.

[0025] It is yet another object of the present invention to provide sucha system which employs unique compounds.

[0026] It is another object of the present invention to provide such asystem which will effectively and rapidly provide corrosion resistanceto steel and other metals.

[0027] It is yet another object of the invention to provide such asystem which may be employed by merely adding one or more compounds ofchoice to fresh concrete without requiring substantial changes inconventional practices employed in producing and placing the concretestructure.

[0028] It is a further object of the present invention to provide such asystem where an existing concrete structure may be rehabilitated bysequestering the chloride and providing a means to accumulate nitriteions in the vicinity of the embedded steel. It is appreciated that thenitrite ions oxidize presently corroding steel to produce a protectivelayer. In some formulations nitrite ions may not be available and inthese instances rehabilitation is the result of chloride sequestrationonly.

[0029] It is yet another object of the present invention to provide sucha system wherein an overlay, which contains a composition which may beof the type employed in other embodiments of the invention andfacilitates sequestering of chloride and corrosion protection of metalstructural elements. In another version, a slurry containing thecompound of interest may be applied to the concrete structure with anoverlay material either formed in situ or as a preformed panel securedthereover.

[0030] It is yet another object of the present invention to provide sucha system for rehabilitation of existing concrete structures withoutrequiring a source of electrical energy to be present on an ongoingbasis during the performance of the method.

[0031] It is a further object of the present invention to provide forcreation of the desired compound in situ in fresh concrete, or as acomponent, or with it, employed with one or more components employed increating the fresh concrete.

[0032] It is yet another object of the present invention to provide insitu creation of the desired compound in the course of creating a slurryor preformed panel employed in remediation existing concrete structures.

[0033] It is yet another object of the present invention to provide forsuch in situ creation of the compound by adding certain materials eitherin solution or in the mixing water employed to prepare the concrete.

[0034] It is yet another object of the present invention to employsources of aluminum other than calcium aluminate cement in creating thedesired compound.

[0035] It is further an object of the present invention to providealternate sources of calcium and aluminum in creating the desiredcompound.

[0036] It is a further object of the invention to provide a compoundcapable of sequestering chloride ions while controlling the amount ofalumina which is added to the concrete.

[0037] These and other objects of the invention will be more fullyunderstood from the following description of the invention withreference to the drawings appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention is further illustrated by the following non-limiteddrawings in which:

[0039]FIG. 1 is a schematic cross-sectional illustration of a concretebridge deck containing metal reinforcing elements.

[0040]FIG. 2 is a schematic cross-sectional illustration similar to FIG.1, but showing a construction having an overlay containing the chloridesequestering composition.

[0041]FIG. 3 is a schematic cross-sectional illustration similar to FIG.2 except that the overlay consists of a slurry adjacent to the concretestructure and an overlaying material.

[0042]FIG. 4 illustrates a cross-sectional illustration looking downwardon a concrete piling which is to be rehabilitated through the system ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] As employed herein the term “concrete structure” refers to anexisting structure which is composed in at least significant part ofconcrete which has set and hardened, as contrasted with “fresh concrete”as defined herein and shall expressly include, but not be limited to,bridges, roadways, parking lots, sidewalks, parking garages, floors,support columns, piers, marine structures, piling, conduits and otherconcrete structures whether located inside or outside, and whethersubject to vehicular or foot traffic thereover or not.

[0044] As employed herein, the term “fresh concrete” means concretewhich is in a plastic state.

[0045] As employed herein reference to “introducing” a compound intofresh concrete shall be deemed to include introducing the compound insolid form and in slurry form with or without other ingredients such asminerals and additives into fresh concrete and shall also embraceadmixing or blending the composition in dry form with dry cement and/orother ingredients prior to water being added.

[0046] As employed herein, the term “metal elements” means metalelements placed within or in contact with concrete for various purposesincluding, but not limited to, structural purposes and shall expresslyinclude, but not be limited to, reinforcing bars, grills, beams, metaldeck hold downs and wire mesh.

[0047] As shown schematically in FIG. 1, a layer of concrete 2, overliesand is supported by a deck member 4. The concrete in the form shown hasa plurality of elongated, generally parallel, reinforcing bars 6, 8, 10,12, 14, 16, 18. This assembly may be created in a conventional manner toprovide the desired structure which, in the form shown, may be a bridgedeck having an undersurface 22, exposed to air 24 and an upper surface26, which may have undesired snow deposited thereon or ice formedthereon. Application of calcium chloride, sodium chloride or otherchloride containing salts to the upper surface 26, or the overlying iceand snow (not shown) results in chloride penetration into the concreteinterior and, if not inhibited, contact with the metal reinforcing bar6-18 (even numbers only) which will generally be composed of steel tocreate the undesired corrosion.

[0048] For convenience of reference herein, the use of metal elementssuch as steel reinforcing bars 6-18 (even numbers only) will bediscussed. It will be appreciated that corrosion inhibition of othertypes of metal elements such as those made of or coated with copper, tinor zinc, for example, may benefit from the present invention.

[0049] In one embodiment of the invention, there is not only providedfree nitrite, which oxidizes ferrous (Fe²⁺) to ferric (Fe³⁺) ion tothereby effect precipitation of Fe₂O₃ to form an iron oxide barrier, butalso provides means to sequester chloride which enters the concreteporosity by capturing the same in low solubility compounds.

[0050] As employed herein the term “low-solubility compounds“ means,chloride-containing compounds exhibiting solubilities substantiallybelow those of sodium chloride or calcium chloride, and shall include,but not be limited to, chloride-containing compounds, which atsaturation in aqueous solutions permit less than about 1 kg of solublechloride per cubic meter of concrete. A chloride level of about 1 kg/m³of concrete is considered the threshold level for corrosion.

[0051] In general, the invention contemplates the addition of anycompound into which chloride ions would enter to produce a lowsolubility compound that sequesters the chloride.

[0052] An example of a preferred reaction of the present invention,which accomplishes both the objective of creating an iron oxide barrierand the sequestering of chloride, is shown in reaction (1).

3CaO.Al₂O₃Ca(NO₂)₂ .nH₂O+2Cl₁

3CaO.Al₂O₃.CaCl₂ .nH₂O+2NO₂.  (1)

[0053] In this example 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O wherein n=10 is added tofresh concrete as a particulate solid. The reaction that occurs is thechloride from the de-icing salts used on the hardened concrete reacts toproduce Friedel's salt, which sequesters the chloride and, in addition,serves to release nitrite in order to oxidize any Fe²⁺. In adding theparticulate compound, 3CaO.A1 ₂O₃.Ca(NO₂)₂.nH₂O, is added to the freshconcrete, it is preferred that in general about 3 to 88 pounds of theparticulate solid will be added per cubic yard of hydrated freshconcrete, and preferably about 22 to 66 pounds of concrete per cubicyard. The exact amount will be influenced by the anticipated rates ofchloride ingress into the concrete having the usual range ofwater-to-cement ratios, e.g., 0.35 to 0.50. The admixture may, ifdesired, be employed in concrete having lower water-to-cement ratiossuch as 0.25 to 0.35, for example, or higher ratios such as 0.5 to 0.9,for example. In general, the higher the anticipated rate of chlorideingress, the larger the amount of particulate composition employed. Thecompound is admixed with the hydrated fresh concrete to achievesubstantially uniform distribution thereof. When the concrete sets, thisconstituent will be present in the concrete to receive and interact withchlorine from the icing salts that penetrates the pores of the concrete.This compound (3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O) is generally stable over therange of pH values normally encountered in concrete. The resultantcompound 3CaO.Al₂O₃.CaCl₂.10H₂O is a low solubility compound withinwhich the chloride is sequestered. This compound, is more stable thanthe nitrite. Chloride will exchange for the nitrite thereby freeing thenitrite and sequestering the chloride. As a result, the concentration ofchloride in the concrete at the surface of the steel, such as re-bars6-18 (even numbers only) will be reduced as compared with concrete notcontaining the compound. This same reaction may be employed with thesame result substituting Fe₂O₃ for Al₂O₃ in the starting material. Thiswould result in the reaction 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O+2Cl

3CaO.Fe₂O₃.CaCl₂.nH₂O+2NO₂

[0054] In lieu of providing the compound such as3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O in dry particulate form, it may be presented asa slurry with a pH of about 10 or greater with the particulate beingpresent in the slurry in the range of about 5 to 60 weight percent andpreferably about 10 to 35 weight percent. The slurry then would beadmixed with the hydrated fresh concrete.

[0055] In lieu of introducing the particulate solid or slurry intohydrated fresh concrete, if desired, one may admix the particulate solidor slurry with one or more of the dry components of the concrete such asthe cement, for example.

[0056] In lieu of the compound employed in reaction (1), other compoundsmay be used to create essentially the same reaction with the followingdifferences. Among these compounds are, 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O whereinn=0 to 24; 3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O wherein n=0 to 24; and3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O wherein n=0 to 24.

[0057] Also, 3Me(II)O.R₂O₃.Me(II)(anion)₂.nH₂O wherein Me(II) is one ormore cations, R₂ is Al₂, Fe₂ or Cr₂, anion is NO₂, NO₃ or OH and n=0 to24 may be employed. These approaches, in many instances, involve asubstitution in the compound employed in equation (1) for the aluminum,for the calcium or the nitrite. As to the substitution for the nitrite,this would be replaced by nitrate in equation (1)3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O or 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O. As statedhereinbefore, the anion may be divalent in which case the formula wouldbe 3Me(II)O.R₂O.Me(II)(anion).nH₂O wherein n is 0 to 18 and preferably10 to 18. In other compositions, nitrite could be replaced by carbonate,borate or other anions.

[0058] The nitrites have the advantage of sequestering chloride inaddition to liberating a species capable of rapidly oxidizing ferrous(Fe²⁺) ions near the surface of corroding seal to ferric (Fe³⁺) ions tofacilitate the formation of a protective layer of ferric oxide orhydroxide on the steel.

[0059] It is understood that the value of “n”, meaning the number ofwaters of hydration, may vary, depending on the relative humidity towhich the compounds are exposed.

[0060] Among the preferred compounds for use in the invention are,3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O and 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O in terms ofeffectiveness for both chloride sequestration in concrete and protectiveoxide layer formation of metal embedded or in contact with concrete. Itis preferred that n=0 to 24.

[0061] In an additional embodiment, the present invention providesmethods of resisting corrosion of metals in concrete comprisingintroducing into concrete having metal elements at least one compoundcapable of sequestering chloride ions, the compound being a combinationcompound having the formula

3Me(II)O.(R, R′)₂O₃.Me(II)(anion)₂ .nH₂O,

[0062] where R and R′ are different and are independently selected fromthe group consisting of Al, Fe and Cr; anion is selected from the groupconsisting of NO₂, NO₃ and OH, n is 0 to 24, and Me(II) is a cation andis selected from the group consisting of Ca, Ba, Sr, Mn, Zn andcombinations thereof. When, for example, Al and Fe are selected, theabove formula can also be written as 3Me(II)O.(Al,Fe)₂O₃.Me(II)(anion)₂.nH₂O. Another example of the chemical formulawould be Ca₂(Al, Fe)(OH)₆(anion).nH₂O (see, e.g., Taylor, HFW, “CementChemistry”, p. 173-176.).

[0063] As used herein, the term “combination compound” is used to referto compounds which exist as a solid solution, a partial solid solution,and/or as a material having areas rich in one element (such as Al, Fe orCr) and other areas rich in another, different element in this group.The combination compound of the present invention can exist in any oneor combination of these states. A solid solution in the context of thecombination compound of the present invention refers to a compound inwhich the oxygen ions arrange themselves to occupy a periodicthree-dimensional array. Al, Fe or Cr atoms then randomly occupylocations within the array.

[0064] Preferably, R is Al and R′ is Fe in the above formula. Al and Fe(or Cr) can be combined in any ratio desired, for example, up to 99% Aland 1% Fe, or 99% Fe and 1% Al, or any desired combination between theseranges.

[0065] The amount of Al, Fe, and/or Cr to be used will depend on theproperties of the cement to which they are added and the end useenvironment. For example, the preferred upper limit on Al in cement tobe used in a “severe sulfate” environment, is a cement containing nomore than 5 wt % of 3CaO.Al₂O₃. Thus, the Al content of the corrosioninhibiting admixture in combination with Al already present in thecement (which varies depending on the type of cement and ingredientsused to make it) should not exceed 5% of the weight of the cement.Cement to be used in a moderate sulfate environment should contain nomore than 8 wt % of 3CaO.Al₂O₃. Thus, the Al content of corrosioninhibiting admixture in combination with that in the cement should notexceed 8% of the weight of the cement (American Concrete Institute.Committee 201 report: Guide to Durable Concrete).

[0066] Preferably, the source of Al₂O₃, Fe₂O₃ or Cr₂O₃ is a solid suchas red mud (which contains alumina and iron oxide), bauxite, any calciumaluminate, for example mono- or tricalcium aluminate, calcium ferrite,calcium alumino ferrite, reactive sources of alumina such as Al₂O₃ orAl(OH)₃. This list is meant to be non-limiting, and any suitable solidsource of Al₂O₃, Fe₂O₃ and Cr₂O₃ can be used.

[0067] In a particularly preferred embodiment, the combination compoundcomprises (Al, Fe)₂O₃, anion is NO₂ or NO₃, and Me(II) is Ca.

[0068] The combination compound can be formed as a particulate by mixingthe selected ingredients in suitable proportions to produce

[0069] 3Me(II).(R, R′)₂O₃.Me(II)(anion)₂.nH₂O. In a preferredembodiment, appropriate combinations of Al₂O₃, Fe₂O₃ or a solid such asred mud (which contains alumina and iron oxide), bauxite, any calciumaluminate, for example mono- or tricalcium aluminate, calcium ferrite,calcium alumino ferrite, reactive sources of alumina such as Al₂O₃ orAl(OH)₃ and supplementary sources of Ca, such as CaO or Ca(OH)₂ and asource of nitrate or nitrite, such as NaNO₂, NaNO₃, Ca(NO₂)₂ or Ca(NO₃)₂are used to make the combination compound. Such formation may occur atroom temperature or elevated temperature. In the event that aNa-containing salt is used, it may be desirable to remove the majorityof any dissolved sodium salt by filtration followed by washing thecombination compound with water.

[0070] The combination compound can be introduced into fresh concrete,or can be mixed with the ingredients used to make concrete, prior to orafter the addition of water. Alternatively, the compound can beintroduced in to fresh or dry concrete as a slurry, or can be introducedinto any of the components used in creating concrete, prior to or afterthe addition to other ingredients. Any of the methods of mixingpreviously described herein are suitable for use with the combinationcompound of this embodiment, provided that, as described below, thecombination compound is made prior to mixing it with concrete orcomponents used to make concrete. The combination compound cannot beefficiently created in situ by mixing the precursor compounds with theconcrete or concrete components.

[0071] The following reaction creates the chloride sequesteringcompound: 3Me(II)O.(R, R′)₂O₃.Me(II)(anion)₂.nH₂O+2Cl

3Me(II)O.(R, R′)₂O₃.Me(II)Cl₂.nH.₂O+2(anion)^(−.)

[0072] When anion is NO₂ ³¹, this reaction will further establish acorrosion resistant oxide layer on the metal elements embedded withinthe concrete. When the anion is NO₃ ⁻, the corrosion-inhibiting effectis limited to chloride sequestration.

[0073] The use of a combination compound permits the sequestration ofchloride ions while controlling the amount of alumina which is added tothe concrete. For applications where concrete is exposed to combinationsof sulfate and chlorides, it is undesirable to increase the reactivealumina content of the cement. This is because sources of reactivealumina can contribute to sulfate attack. Seawater, for example,contains both sulfates and chlorides. If chloride is able to enter thepore structure of the concrete, sulfate will also be able to enter. Itis desirable to be able to sequester the chloride without causingsulfate attack. Some reactive alumina is tolerable. For example sulfateresisting cement is permitted to contain small amounts of reactivealumina, as describe above.

[0074] The alumina compounds 3Me(II)O.Al₂O₃.Me(II)(anion)₂.nH₂O arereadily formed under a variety of circumstances. The iron compounds3Me(II)O.Fe₂O₃.Me(II)(anion)₂.nH₂O form more slowly. The combinationcompound, 3Me(II)O.(Fe, Al)₂O₃.Me(II)(anion)₂.nH₂O exhibits intermediatebehavior. Thus, the presence of reactive alumina facilitates theformation of the compounds of interest while the presence of iron oxideavoids the problem of promoting sulfate attack. The compounds are formedseparately as follows: The nitrate-based chloride sequestering compound3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O can be produced in the manner described aboveusing tricalcium aluminate, or monocalcium aluminate and calciumhydroxide:

[0075] The compounds 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O and3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O are produced using 2CaO.Fe₂O₃ in the presencesupplementary Ca from Ca(OH)₂ and nitrite or nitrate from their calciumand/or sodium salts. 2CaO.Fe₂O₃ is produced by blending Fe₂O₃ and CaCO₃in a molar ratio of 2:1 followed by sintering this mixture at 1150° C.for approximately 1.5 hours. The mixture of CaO and 2CaO.Fe₂O₃ isproduced by calcining 1 mole of CaCO₃ with 3 moles of Fe₂O₃ at 1100° C.for ˜1.5 hour. A variety of reaction times and temperatures can be usedin the synthesis of this compound or this mixture. After cooling the2CaO.Fe₂O₃ or the mixture of 2CaO.Fe₂O₃ and CaO are ground to an averageparticle size of approximately 10 microns using ordinary comminutiontechniques.

[0076] The combination compound is made by forming a physical mixture of3CaO.Al₂O₃ or CaO.Al₂O₃ and 2CaO.Fe₂O₃ and with suitable proportions ofadditional CaO or Ca(OH)₂ and nitrate or nitrite compounds. Thus to make3 CaO.(Fe_(1.0) Al_(1.0))O₃.CaNO_(y).nH₂O, equimolar proportions of2CaO.Fe₂O₃ and 3CaO.Al₂O₃ or CaO.Al₂O₃ will be added to the appropriateproporations of nitrate, or nitrite and CaO or Ca(OH)₂. The Al and Fereactants are particulate solids, ground to high fineness (typically3500 cm²/g) or to a average particle size of 5-10 microns. Reaction maybe carried out at any temperature above freezing. This includes reactionunder steam pressure at hydrothermal conditions, provided the containeris sealed. Upon mixing, the components further react to form a solidsolution, and do not remain as a simple physical mixture.

[0077] Thus, in additional aspect, the present invention provides amethod of making a compound which sequesters chloride ions and providesresistance to corrosion of metals in concrete. The method comprisesmixing a solid source of aluminum, iron, or chromium oxide or hydroxide,or combinations thereof, with a cation and an anion under suitableconditions as described above, to provide a compound having the formula

3Me(II)O.R₂O₃.Me(II)(anion)₂ .nH₂O

[0078] where R is selected from the group consisting of Al, Fe or Cr andcombinations thereof, anion is NO₂, NO₃ or OH, n=0 to 24, and Me(II) isa cation selected from the group consisting of Ca, Ba, Sr, Mn, Zn andcombinations thereof. In this embodiment, R can be a single elementselected from the group Al, Fe or Cr, or can be at least two differentelements selected from this group. When more than one of these elementsis used, the combination compound described above will result. The abovecompound can be added to concrete, or to overlays provided on top of theconcrete, or to both structures.

[0079] In a further embodiment, the present invention provides aconcrete structure comprising concrete, a plurality of metal elements incontact with said concrete, and a compound capable of sequesteringchloride ions having the formula

3Me(II)O.(R, R′)₂O₃.Me(II)(anion)₂.nH₂O,

[0080] where R and R′ are different and are independently selected fromthe group consisting of Al, Fe and Cr; anion is selected from the groupconsisting of NO₂, NO₃ and OH, n is 0 to 24, and Me(II) is a cation andis selected from the group consisting of Ca, Ba, Sr, Mn, Zn andcombinations thereof, disposed within said concrete. The concretestructure can be a bridge, a pier, a portion of a highway, a portion ofa parking garage or parking lot, or any concrete structure havingreinforcing metal elements. An overlay can be formed on the concretestructure, and can be secured to the concrete structure by any means,including, for example, adhesive. The overlay can be preformed ifdesired, or can be applied as a slurry and allowed to set. An additionalsecond layer, over the overlay, can also be used, to provide additionalprotection to the concrete structure. In yet a further embodiment aconcrete assembly is provided, comprising a concrete structure having aplurality of metal elements and an overlay disposed in close adjacencyto the concrete structure. The concrete structure and/or the overlaycontain the combination compound as described above.

EXAMPLES

[0081] The following examples are intended to illustrate the inventionand should not be construed as limiting the invention in any way.

[0082] In order to provide more detailed information regarding themanner of synthesizing the compounds, examples will be provided.

[0083] In the synthesis of 3 CaO.Al₂O₃.Ca(NO₂)₂.nH₂O wherein n=0 to 24,the following procedure may be followed.

[0084] In employing 3 CaO.Al₂O₃ the following process of synthesis maybe employed:

[0085] The presence NaOH does not appear to interfere with sequestrationof chloride or with the action of nitrite on steel and, as a result, itis not necessary to remove the NaOH by washing the product compounds.Alternatively, the solid 3 CaO.Al₂O₃ and Ca(NO₂)₂.nH₂O can be separatedfrom the NaOH solution by washing and/or filtration.

[0086] In each of these two examples, the Ca(OH)₂ and calcium aluminatewere employed as fine powders. Ca(NO₂)₂ and NaNO₂ are commerciallyavailable and highly soluble in water. While there are no criticalparticle size distributions, in general, it is preferred to have aparticle size such that 99% of the powder passes through a 325 meshsieve. Commercially available Ca(OH)₂ was employed as was commerciallyavailable CaO.Al₂O₃ with the latter being employed as a refractorycement. The synthesis in each case was carried out at room temperatureby mixing the reactives with approximately 10 times their weight ofwater in suitable sealed containers. Their reaction occurred morerapidly if the contents of the containers were stirred or agitated.Optionally, if desired, grinding media such as Zirconia media, forexample, may be placed in the containers.

[0087] The nitrate-based chloride sequestering compound3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O wherein n=0 to 24 can be produced in the mannerdescribed in the foregoing two examples employing tri-calcium aluminateor mono-calcium aluminate and calcium hydroxide.

[0088] In using 3CaO.Al₂O₃ as a starting material, the following processcan be employed:

[0089] wherein n=0 to 24.

[0090] Employing CaO.Al₂O₃ as the starting material, the followingprocess can be employed.

[0091] wherein n=0 to 24.

[0092] The presence NaOH does not appear to interfere with sequestrationof chloride or with the action of nitrite on steel and, as a result, itis not necessary to remove the NaOH by washing the product compounds.Alternatively, the 3CaO.Al₂O₃.Ca(NO₃)₂.nH₂O and Ca(NO₃)₂ can beseparated from the NaOH solution by washing and/or filtration.

EXAMPLE 2

[0093] The phase 3CaO.Fe₂O₃.CaCl₂.nH₂O wherein n=10 has been created byreacting the precursors 3 CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O and 3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O with chloride. This indicates that chloride ionscan be sequestered in the Fe analog of Friedel's salt (3CaO.Al₂O₃.CaCl₂.10H₂O). The compounds 3CaO.Fe₂O₃.Ca(NO₂)₂.nH₂O and 3CaO.Fe₂O₃.Ca(NO₃)₂nH₂O have also been produced employing 2CaO.Fe₂O₃. in thepresence of supplementary Ca from Ca(OH)₂ and nitrite or nitrate fromtheir calcium and/or sodium salts. 2CaO.Fe₂O₃ may be produced byblending Fe₂O₃ and CaCO₃ in a molar ratio of about 2:1 followed bysintering this mixture at 1150° C. for approximately 1.5 hours. Themixture of CaO and 2CaO.Fe₂O₃ is produced by calcining 3 moles of CaCO₃with 1 mole of Fe₂O₃ at 1100° C. for approximately 1.5 hours. A varietyof reaction times and temperatures can be used in the synthesis of thiscompound or this mixture. After cooling the 2CaO.Fe₂O₃ or the mixture of2CaO.Fe₂O₃ and CaO were ground to an average particle size ofapproximately 10 microns using known comminution techniques.

EXAMPLE 3

[0094] The compounds 3CaO.Fe₂O₃.Ca(NO₃)₂.nH₂O may be produced bycalcining 1 mole of CaCO₃ with 3 moles of Fe₂O₃ at 1100° C. for about1.5 hours. This produces a mixture of CaO and 2 CaO.Fe₂O₃. This mixtureis then ground and reacted with either NaNO₃ or Ca(NO₃)₂ under basicconditions. In the event that NaNO₃ is used, it is necessary to addsupplemental calcium for the reaction to go to completion. This may beadded as CaO or Ca(OH)₂ for example.

[0095] With respect to compound 3Me(II)O.(R₁, R₂)₂O₃(Me(II)(anion)₂.nH₂Owherein R₁ and R₂ are Al, Fe or Cr, anion is NO₂, NO₃ or OH and n is 0to 24 where Me(II) is a cation such as Ca, anion may be partiallysubstituted by other divalent cations or may be completely substitutedby other divalent cations such as Ba, Sr, Mn, Zn, for example. For somecompositions divalent anions such as carbonate or borate may be used.

[0096] Referring to FIG. 2, wherein an existing concrete structure 2having reinforcing metal elements 6-18 (even numbers only) is shown withan underlying deck member 4, which may or may not be present inconnection with the rehabilitation of existing concrete structures asprovided in this embodiment of the invention. An overlay 30, which inthe form illustrated, it is concrete containing a compound usable in thepresent invention to sequester chloride ions with or without thecapability of releasing nitrites to establish an oxide coating on themetal reinforcing member 6-18 is shown. This overlay 30 preferably has aporosity similar, or in excess of, to that of the concrete in thestructure so as to permit free movement of chloride ions and nitritestherebetween. The thickness T of the overlay 30 may be in the order of0.5 to 10 inches with a preferred thickness being about 1-4 inches.

[0097] The overlay 30 may be established in situ and self-bonded to theupper surface 32 of the concrete structure. In the alternative, theoverlay 30 may be a preformed panel containing the compound which may besecured to the concrete structure 2 by any desired means such as anadhesive material preferably provide a continuously between the overlay30 and the concrete layer 2 without interfering meaningfully withporosity in the interchange between the two structural elements or maybe provided in certain locations leaving other areas forsurface-to-surface contact between the overlay 30 and the concretemember 2. A suitable adhesive for this purpose is latex.

[0098] In lieu of the concrete material employed in overlay 30, othersuitable materials having the desired strength, porosity and othercharacteristics needed for the present invention, may be employed. Amongthese are asphaltic materials, clay and clay-like materials and othercement materials including but not limited to Portland cements, blendsof Portland cement with other materials such as fly-ash, slag or silicafume, calcium aluminate cements and mortars.

[0099] The overlay 30 provides a number of beneficial actions, whichfacilitate rehabilitation of the existing concrete structure 2. First ofall, chloride will migrate out of the concrete 2 in response to theconcentration gradient produced in the pore structure of the concrete 2,the pore structure across the interface with the overlay 30 and with thepore structure of the overlay 30 itself The admixture in the overlay 30sequestered chloride ions that enter the overlay 30. Nitrite willmigrate from the overlay 30 into the concrete 2 and toward thereinforcing steel 6-18 (even numbers only) in response to theconcentration ingredient produced in the pore structure of the concreteitself, in the pore structure across the interface at surface 32 betweenthe concrete 2 and overlay 30 and within the pore structure of theoverlay 30 itself. The nitrite facilitates formation of a protectivecoating on the metal reinforcing elements 6-18, which may be composed ofsteel. All of this is accomplished without requiring prior art externalelectric current application. The system, therefore, results in passivechloride extraction.

[0100] If desired, in order to enhance the efficiency of maintaining thedesired continuous moisture path, through which the chloride ions andnitrite can move, additional wetting may be applied and a low porosityoverlay (not shown) overlying the upper surface 33 of the overlay 30 maybe provided in order to seal the moisture in the structure. Also, rainmay enhance such moisture paths. The low porosity overlay may be appliedas a self-bonding coating established in situ or as a preformed elementsecured to surface 33.

[0101] In employing the process in connection with FIG. 2 and theembodiment describing in connection with FIG. 3, the compoundspreviously disclosed herein may be employed. It will be understood thatthose compounds which both sequester chloride ions and release nitritewill result in both the sequestration of chloride ion and releasing ofnitrite serving to create the protective oxide layer around the metalreinforcing members 6-18 in the manner described herein.

[0102] Referred to FIG. 3, there is shown an embodiment similar to thatof FIG. 2 except that the overlay 30 has a lower portion which is aseparately formed slurry 34 disposed between the upper surface 32 ofexisting concrete structure 2 and the upper portion of overlay 30 withthe overall thickness of the overlay 30 remaining within the range ofthickness T. The slurry will be porous to facilitate migration ofchloride ions and nitrite between it and the underlying concretestructure 2. The porosity of the slurry 34 will be such as to maintaincommunication with the underlying concrete 2. The slurry 34, which maybe employed alone (not shown) or in combination with another portion ofoverlay 30 as shown in FIG. 3, will contain the compound employed toeffect the objectives of the invention and may also include cements andsand as desired. In cases where slurry 34 is employed preferably aloneit has a thickness of about {fraction (1/8)} inch to 4 inches. Ingeneral, the water to solids ratio of the slurry will facilitate itsbeing pumpable or spreadable with the capability of hardening with theconsumption of free water during formation of 3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O,wherein n=0 to 24. The water to solids ratios may be about 0.25-5 andpreferably about 0.4 to 1.0. The slurry is pumped, sprayed, troweled orotherwise placed on the surface 32 to create slurry layer 34. Thethickness of the slurry preferably will be in the range of about 0.125to 4 inches and if sand is not present in the composition, willpreferably be in the range of about 0.25 to 0.5 inch. With sand, therange is preferably about 0.5 to 1.0 inch. It will be appreciated thatif in lieu of the composition previously recited in this paragraph, thecomposition 3 CaO.Al₂O₃.Ca(NO₃)₂.nH₂O, wherein n=0 to 24 were employedas nitrate is not regarded as a corrosion inhibitor in the sense ofcreating an oxide protective coating on the metal elements, thiscompound would provide solely a means for removing chloride ions fromthe concrete, but not inhibition of corrosion of embedded steel or othermetal. The amount of the compound employed in a specific installationcan be determined by the amount of chloride that has entered theconcrete structure and can be determined readily by those skilled in theart.

[0103] Referring to an embodiment wherein the vertical concretestructural be remediated, FIG. 4 shows a piling 40 which is generallyvertically oriented and may be located under water. It has a pluralityof elongated steel reinforcing members 42, 44, 46, 48, 50 embeddedtherein. A continuous clamshell 60 has been placed around the piling 40to create an annular region 64 within which a slurry of the presentinvention may be introduced. The clamshell 60 may be in segments whichare longitudinally adjacent to each other and secured to each other.They may be joined by bolts or other suitable mechanical means such ascables, or clamps. The annular region 64 has the slurry introduced afterthe clamshell 60 is placed in the space with the slurry being pumped into displace water within an annular region 64. In other respects, thesystem of the invention performs in the identical manner as previouslydescribed herein.

[0104] It will be appreciated that depending upon the specific nature ofthe concrete structure to be remediated and the location and nature ofthe environment in which it is being employed, certain preferredrefinements of this embodiment of the invention may be employed. Forexample, in situations where vehicular or foot traffic may be imposed onthe concrete structure and an overlay with high strength should to beprovided. Also, for example, in situations were the concrete structurewill be subjected to a freeze-thaw cycles certain preferred approachesmay serve to minimize the effects of the same. For example, anair-entrained admixture may be provided in slurry 34 of FIG. 3 tocounteract the effects of the freeze-thaw cycles. Such an approach mightinvolve adding a chemical in a small amount, such as about 0.1% of theweight of the concrete, for example, to produce small bubbles when theconcrete freezes the water in the porosity migrates into the bubbles andfreezes harmlessly.

[0105] An alternate way of minimizing the effect of the freeze-thawcycle would be maintain a high ionic strength liquid in the porosity ofthe slurry. The more ions dissolved in water the lower the freezingtemperature. For example, soluble nitrite salts such as calcium nitrite,calcium nitrite, sodium nitrate, or sodium nitrite may be employed forthis purpose and function to increase the concentration ingredient innitrite and thereby facilitate movement of nitrite into the concrete.

[0106] Another compound suitable for use in the present invention wouldinvolve the use of the source of aluminum not coming from cement. Thiswould result from the use of sodium aluminate NaAlO₄. This may beaccomplished by the following approaches.

2NaAlO₄+3Ca(OH)₂+Ca(NO₂)₂→3CaO.Al₂O₃.Ca(NO₂)₂ .nH₂O+2NaOH  (A)

[0107] wherein n=0 to 24 and preferably 0 to 12

[0108] or

2NaAlO₄+4Ca(OH)₂+2NaNO₂→3CaO.Al₂O₃.Ca(NO₂)₂ .nH₂O+4NaOH  (B)

[0109] wherein n=0 to 24 and preferably 0 to 12.

[0110] In certain embodiments of the invention, the aluminum constituentwas provided in alumina form from calcium aluminate cement (CaO.Al₂O₃),or tricalcium aluminate cement (3 CaO.Al₂O₃). Other sources may beemployed. The alternate materials could be a source of alumina,aluminate or aluminum hydroxide having sufficient reactivity to form thedesired admixture. For example, an alumina selected from the groupconsisting of alpha alumina, flash calcined alumina, and transitionaluminas may be employed. Transition aluminas include gamma alumina,theta alumina, and kappa alumina, for example. Other calcium aluminatessuch as CaO.2Al₂O₃ or CaO.6 Al₂O₃ for example, could be employed.Suitable aluminates would include a source containing the AlO₂ ⁻ ion andother alumina salts. Among the suitable aluminates are sodium aluminateand potassium aluminate.

[0111] Among other sources are organo-aluminates, such as sec-butoxidefor example. Other suitable sources are aluminum hydroxides such asnon-crystalline gels, forms of Al(OH)₃ such as gibbsite or bayerite,forms of AlOOH such as boehmite or diaspore and other hydrated aluminassuch as tohdite (5 Al₂O₃.H₂O).

[0112] In another embodiment of the invention, a slurry or preformedpanel containing a source of calcium such as Ca(OH)₂ and a source ofalumina such as CaO.Al₂O₃ or 3CaO.Al₂O₃ which is either premixed withthe calcium source or applied separately, is applied over a concretestructure to sequester chloride ions from the concrete structure. Anexample of such a method of producing such an overlay is the followingreaction.

CaO.Al₂O₃+3Ca(OH)₂ +nH₂O→3CaO.Al₂O₃.Ca(OH)₂ —nH₂O

[0113] wherein n=0 to 24 and preferably 12 to 18.

[0114] The reaction product will convert to 3CaO.Al₂O₃.Ca(Cl)₂.nH₂O

[0115] wherein n=0 to 24 when it sequesters the chloride ion from theconcrete structure.

[0116] It will be appreciated, therefore, that the present invention hasprovided an effective method and related compounds and structure forincorporating into concrete containing metal elements a class ofcompounds which will effectively resist undesired corrosion of themetallic compounds by both sequestration of chloride ions and provide acoating on the metallic elements, in some instances such as reactionsthat release nitrite. Other reactions, such as those which releasenitrate alone, occur without providing such a coating.

[0117] It will be appreciated that the compositions of the presentinvention may be combined with fresh concrete as defined herein in manyways. For example, the composition may be combined in solid form (a)with concrete in a plastic state (b) with ready mix concrete at a jobsite (c) at the time of batching or (d) inter-blended with mineraladmixtures of materials such as slag, fly ash, or silica fume, or (e)may be interblended with cement, for example. It may also be combined inslurry form in a suitable liquid such as Ca(OH)₂ solution at the time ofbatching, for example. These approaches are all within the scope of thepresent invention.

[0118] In another embodiment of the invention, the chloride ionsequestering component or chloride ion sequestering and nitritereleasing compound may be created in situ. The compound3CaO.Al₂O₃.Ca(NO₂)₂.nH₂O and similar compounds having the desiredchloride ion sequestering or chloride ion sequestering and nitritereleasing capability may be created in this manner.

[0119] One manner of effecting creation of the desired compound in situwould be to add a solution containing NaAlO₄, Ca(NO₂)₂ and/or NaNO₂ tomixing water to be employed to prepare fresh concrete. Alternatively,the added materials could be mixed directly with the water. Duringcement hydration, Ca(OH)₂ would be produced and would react with theadded materials such as in reactions A and B. This results in in situcreation of a compound that both sequester chloride ion and releasesnitrite.

[0120] As another approach, in lieu of relying on the concrete hydrationto provide the Ca(OH)₂, it may be admixed with one or more of NaAlO₄,Ca(NO₂)₂ and NaNO₂ and, be added to fresh concrete or to the mixingwater employed to prepare the fresh concrete.

[0121] Another approach to in situ creation would be to add calciumaluminate cement along with NaNO₂ or Ca(NO)₂ with or without Ca(OH)₂ tothe concrete making materials to create 3 CaO.Al₂O₃.Ca(NO₂)₂nH₂O in situwherein n=0 to 24 and preferably 12 to 18.

[0122] These general approaches may be employed in creating a slurry forremediation of concrete structures by mixing Ca(OH)₂ with NAlO₄,Ca(NO₂)₂ and/or NaNO₂ and providing the same on existing concrete. Thissame approach can be employed in creating pre-formed overlay panels foruse in remediation.

[0123] The hereinbefore described alternate sources of aluminum may beemployed in this in situ embodiment along with NaNO₂ and/or Ca(NO₂)₂.

[0124] An alternate approach to the in situ embodiment would be toemploy nitrate salts such as NaNO₃ or Ca(NO₃)₂ which would produce acompound that sequestered chloride ions, but would not yield nitriteswhich would result in an oxide protective layer on the metal elements.

[0125] In another embodiment of the invention employed to remediate aconcrete structure, a solution containing a soluble source of alumina,such as NaAlO₄, for example, is combined within a solution, which may bean aqueous solution, with at least one material selected from the groupconsisting of Ca(NO₂)₂ and NaNO₂. This solution is introduced into thepores of the concrete structure to effect chlorine ion sequestrationwithin the concrete structure. The components would react with eachother and the Ca(OH)₂ contained within the concrete in order to producethe corrosion inhibiting compound. The nitrite which results from thereaction will serve to effect the creation of oxide protective layer onthe metal elements in the manner described hereinbefore. The solutionmay be introduced under pressure or by capillary suction after placingthe solution on the concrete surface, for example, thereby creating apressurized introduction into the pores. In the alternative, while notpreferred the solution may be allowed to infiltrate the pores under theinfluence of gravity.

[0126] It will further be appreciated that the present inventionprovides a system for rehabilitation of an existing concrete structurethrough an overlay which contains compounds which serve to sequesterchloride ions. It may also establish an oxide barrier layer on metalstructural members associated with the concrete structure.

[0127] Certain preferred compounds have been disclosed herein, alongwith their method of use and resultant structure.

EXAMPLE 4

[0128] The compounds 3CaO.(Fe, Al)₂O₃.Ca(NO₂)₂nH₂O may be produced usinga solid source calcium ferro aluminate compound containing of Al and Feof the composition Ca₂(Al_(x)Fe_(l-x))O₅ where x is between 0 and 0.7.(Taylor, Cement Chemistry (1990) p. 28). The above-named range ofcompositions Ca₂(Al_(x)Fe_(1-x))O₅ can be produced by calciningappropriate proportions of CaCO₃ Fe₂O₃ and Al₂O₃ at about 1250° C. forabout 2 hours. Optionally, if sufficient CaCO₃ is used, a mixture of CaOand Ca₂(Al_(x)Fe_(1-x))O₅ will be produced and it will not be necessaryto add supplemental CaO or Ca(OH)₂ during the reaction which forms 3CaO.(Fe,Al)₂O₃.Ca(NO₂)₂.nH₂O. This mixture is then ground and reactedwith either NaNO₃ or Ca(NO₃)₂ under basic conditions. In the event thatNaNO₃ is used, it is preferred to add supplemental calcium. This may beadded as CaO or Ca(OH)₂ for example.

[0129] Whereas particular embodiments of this invention have beendescribed above for purposes of illustration, it will be evident tothose skilled in the art that numerous variations of the details of thepresent invention may be made without departing from the invention asdefined in the appending claims.

What is claimed is:
 1. A method of resisting corrosion of metals inconcrete comprising: introducing into concrete having metal elements atleast one compound capable of sequestering chloride ions, the compoundbeing a combination compound having the formula 3Me(II)O.(R,R′)₂O₃.Me(II)(anion)₂ .nH₂O, where R and R′ are different and areindependently selected from the group consisting of Al, Fe and Cr; anionis selected from the group consisting of NO₂, NO₃ and OH, n is 0 to 24,and Me(II) is a cation and is selected from the group consisting of Ca,Ba, Sr, Mn, Zn and combinations thereof.
 2. The method of claim 1wherein said chloride sequestration results in a chloride-containingcompound having low solubility in said concrete.
 3. The method of claim1 wherein said anion is NO₂ cation is Ca, R is Al and R′ is Fe.
 4. Themethod of claim 1 wherein said concrete is fresh concrete and saidcompound is introduced in an amount of about 3 to 88 pounds ofparticulate solid per cubic yard of hydrated fresh concrete.
 5. Themethod of claim 1 wherein R and R′ are derived from solid sources. 6.The method of claim 1 wherein the ratio of R to R′ is about 1:1.
 7. Themethod of claim 1 wherein the following reaction creates thechloride-sequestering compound and establishes said corrosion resistantoxide layer: 3 Me(II)O.(R, R′)₂O₃.Me(II)(NO₂)₂. H₂O+2Cl

−

3 Me(II)O.(R, R′)₂O₃.Me(II)Cl₂.nH₂O+2NO₂ ⁻.
 8. A concrete structurecomprising: concrete, a plurality of metal elements in contact with saidconcrete, and a combination compound capable of sequestering chlorideions having the formula 3Me(II)O.(R, R′)₂O₃.Me(II)(anion)₂.nH₂O, where Rand R′ are different and are independently selected from the groupconsisting of Al, Fe and Cr; anion is selected from the group consistingof NO₂, NO₃ and OH, n is 0 to 24, and Me(II) is a cation and is selectedfrom the group consisting of Ca, Ba, Sr, Mn, Zn and combinationsthereof, disposed within said concrete.
 9. The concrete structure ofclaim 8 wherein said anion is NO₂ cation is Ca, R is Al and R′ is Fe.10. The concrete structure of claim 8 wherein said chloride ionsequestering results in a compound having low-solubility in saidconcrete.
 11. A combination compound capable of sequestering chlorideions having the formula 3Me(II)O.(R, R′)₂O₃.Me(II)(anion)₂.nH₂O, where Rand R′ are different and are independently selected from the groupconsisting of Al, Fe and Cr; anion is selected from the group consistingof NO₂, NO₃ and OH, n is 0 to 24, and Me(II) is a cation and is selectedfrom the group consisting of Ca, Ba, Sr, Mn, Zn and combinationsthereof.
 12. The compound of claim 1 wherein the following reactioncreates the chloride sequestering compound: 3 Me(II)O.(R,R′)₂O₃.Me(II)(anion)₂.nH₂O+2Cl³¹ →3Me(II)O.(R,R′)₂O₃.Me(II)Cl₂.nH₂O+2(anion)^(−.)
 13. A method of resisting corrosionof metals in a concrete structure comprising: creating an overlaycontaining at least one combination compound capable of sequesteringchloride ions having the formula 3Me(II)O.(R,R′)₂O₃.Me(II)(anion)₂.nH₂O, where R and R′ are different and areindependently selected from the group consisting of Al, Fe and Cr; anionis selected from the group consisting of NO₂, NO₃ and OH, n is 0 to 24,and Me(II) is a cation and is selected from the group consisting of Ca,Ba, Sr, Mn, Zn and combinations thereof; securing said overlay adjacentto said concrete structure, and sequestering chloride ions in saidoverlay.
 14. The method of claim 13 wherein said overlay is created onsaid concrete structure.
 15. The method of claim 13 wherein said overlayis preformed and then secured to said concrete structure.
 16. The methodof claim 13 wherein said preformed overlay is secured to said concretestructure by adhesive.
 17. The method of claim 13 including applyingsaid overlay to said concrete structure as a slurry.
 18. The method ofclaim 13 including applying a second layer over said slurry overlay. 19.The method of claim 13 including providing said second layer with lowerporosity than said slurry overlay.
 20. The method of claim 13 includingemploying a material selected from the group consisting of concrete,asphalt, Portland cement, clay, calcium aluminate cement, and mortar insaid overlay.
 21. The method of claim 13 including introducing highionic strength liquid into said overlay.
 22. The method of claim 13including employing said method in a concrete structure disposed atleast partially under water.
 23. The method of claim 13 includingperforming said method without requiring ongoing input of electricalenergy.
 24. The method of claim 13 including establishing said overlaywith a thickness of about 0.5 to 10 inches.
 25. The method of claim 13including establishing said overlay with a thickness of about 1 to 4inches.
 26. A concrete assembly comprising: a concrete structure, aplurality of metal elements within said concrete structure and anoverlay, said concrete structure and/or said overlay containing acompound capable of sequestering chloride ions having the formulaMe(II)O.(R, R′)₂O₃.Me(II)(anion)₂.nH₂O, where R and R′ are different andare independently selected from the group consisting of Al, Fe and Cr,anion is selected from the group consisting of NO₂, NO₃ and OH, n is 0to 24, and Me(II) is a cation and is selected from the group consistingof Ca, Ba, Sr, Mn, and Zn, and combinations thereof, and said concretestructure and said overlay being disposed in close adjacency to permition exchange between pores of said concrete structure and said overlay.27. The concrete assembly of claim 26 wherein said chloridesequestration results in a chloride-containing compound having lowsolubility in said concrete.
 28. The concrete assembly of claim 26wherein R is Al, R′ is Fe, Me(II) is Ca, and anion is NO₂.
 29. Theconcrete assembly of claim 26, wherein the following reaction createsthe chloride-containing compound and sequesters said chloride ions: 3Me(II)O.(R, R′)₂O₃.Me(II)(anion)₂.nH₂O+2Cl⁻ →3 Me(II)O.(R, R′)₂O₃.Me(II)Cl₂ .nH ₂O+2(anion)⁻.
 30. A method of making a compound whichsequesters chloride ions and provides resistance to corrosion of metalsin concrete comprising mixing a solid source of aluminum, iron orchromium oxide or hydroxide with a cation and an anion to provide acompound having the formula 3Me(II)O.R₂O ₃.Me(II)(anion)₂.nH₂O where Ris selected from the group consisting of Al, Fe, Cr and combinationsthereof, anion is NO₂, NO₃ or OH; n=0 to 24; and Me(II) is a cationselected from the group consisting of Ca, Ba, Sr, Mn, Zn andcombinations thereof.
 31. The method of claim 30, wherein said cation isCa and said anion is NO₂.
 32. The method of claim 30, wherein saidcation is Ca and said anion is NO₃.